This application claims the priority of German Patent Document No. 102 10 898.6, filed 8 Mar. 2002, and PCT/EP03/02068, filed 28 Feb. 2003 the disclosure of which is expressly incorporated by reference herein, respectively.
The present invention relates to an arrangement for sterilizing objects by a low-pressure plasma, including an evacuable chamber for taking up the objects, which evacuable chamber can be connected to a conduit for gas to be ionized, and including a high frequency transmitting device with an antenna system for inductive generating of an alternating current plasma in the chamber.
The sterilizing effect of a plasma lies in a mechanical destruction of microorganisms by a ion bombardment, and further in a chemical destruction by occuring radicals as well as destruction by ultraviolet light. Using a minimum of energy, the plasma can penetrate into the smallest surface cracks and holes, whereby with increasing low pressure, the temperature can be reduced to such an extent that even heat-sensitive objects, for example medical implants containing plastic, can be processed.
There are several possibilities for generating the high frequency power in the chamber, of which, when a particularly high electron density is required, the inductive plasma generating method has proven to be favourable. Antenna systems for inductive generating of an alternating current plasma usually include a ring antenna in the form of a plasma generating coil, whereby an alternating magnetic field positioned perpendicularly on the coil surface, induces an electrical field, which generates, in the gas to be ionized, a electrodeless ring discharge similar to a transformer secondary winding.
Known arrangements using inductive generation of an alternating current plasma in the area of a bordering wall in a chamber have the disadvantage whereby, with increasing distance to the plasma generating coil in the chamber, a strongly inhomogeneous distribution of the electron density is generated, so that objects in close proximity to the high-frequency plasma generating coils are plasma-treated more intensively than those at a distance further away.
It is an object of the present invention to improve the homogeneity of the electron density distribution in the chamber in order that the objects to be sterilized are more evenly treated by the low pressure plasma, in particular in the instance of larger, three-dimensional extension of the objects.
This object has been achieved in accordance with the present invention in that the antenna system includes two plasma generating coils set at a distance apart from one another.
In contrast to known chambers, which, for the purposes of sterilizing objects by low-pressure plasma, use only one plasma generating coil for inductive generating of an alternating current plasma, the arrangement according to the present invention results in a significantly more even electron density distribution. When a given, defined distance is provided between the two plasma generating coils, the electron density distribution of the two plasma generating coils superimpose and accumulate the distribution so that in a larger space between said coils, an electron density is achieved which is, substantially constant. This is particularly true when the distance between the plasma generating coils corresponds approximately to the diameters of the coils. This distance should ideally exceed the extension of the objects to be sterilized. This can be achieved by location of the plasma generating coils in the area of two bordering walls of the chamber, which walls are disposed opposite one another.
The design of the plasma generating coils themselves is irrelevant. Planar or spiral-shaped plasma generating coils can be used advantageously on the bordering walls of the chamber. A possible alternative is to wind helix-shaped plasma generating coils in the area of the bordering walls of the chamber around the chamber.
According to the alternating current plasma of the present invention, large-volume objects can be sterilized, whereby the achievable reduction in microorganisms per time interval on the overall surface is at least approximately the same. The arrangement according to the present invention is therefore particularly advantageous for medical purposes, for example for the sterilizing of implants and bone replacement material as well as medical devices such as sets of instruments, endoscopes or syringes.
In addition to relatively short sterilization times, which, according to the material of the objects, lie in the range of between several tens of seconds and approximately 20 minutes, further positive side effects arise from the arrangement according to the present invention:
In the case of hip implants, which are usually composed of a material combination of titan or ceramic for the ball and ultrahigh molecular polyethylene for the socket, an intended surface modification of the polyethylene can be achieved in that the wear behaviour of the surface is purposely reduced. The thickness of the modified layer is hereby controllable by the reaction time of the plasma.